Computing devices often have some sort of communication interface to provide communication capability to the outside world. In today's market place, these communication interfaces must be easy to use and have the ability to transmit and receive as many bits of information as possible over a given period of time. One type of communication interface that exists today allows communication without the use of wires by transmitting and receiving modulated IR radiation over an air medium. Devices that have this type of interface are often called IR devices. In order to permit IR communication between different brands and types of IR devices, industry wide standards have been developed by groups such as the Infrared Data Association (IRDA).
FIG. 1 depicts a prior art IR device 17 adhering to IRDA standards and having an IR transceiver 19. Transceiver 19 is comprised of IR receiver 23 and IR transmitter 21. The communication link between IR device 17 and a second IR device (also adhering to IRDA standards) is physically accomplished by the alignment of transceiver 19 with the transceiver of the second IR device in a manner that modulated IR radiation emitted from transmitter 21 is detected by the IR receiver of the second IR device. In addition, modulated IR radiation emitted from the IR transmitter of the second IR device is detected by receiver 23. The two IR devices interpret the detected modulated IR radiation as data and control packets in compliance to a predetermined standard set by the IRDA.
The distance between transmitter 21 and receiver 23 is mandated by an IRDA standard. This IRDA standard positions transmitter 21 relative to receiver 23 so that receiver 23 is able to detect IR radiation from transmitter 21. Receiver 23 is referred to as being IR coupled to transmitter 21.
The effect of IR coupling is illustrated in FIG. 2 in conjunction with FIG. 1. Turning now to FIG. 2, two waveforms are shown. The top waveform 37 depicts the status (on or off) of transmitter 21 (FIG. 1). The lower waveform 41 depicts the status (on or off) of receiver 23 (FIG. 1). When transmitter 21 (FIG. 1) is turned on at t=0 (43), transmitter 21 (FIG. 1) begins to emit IR radiation. Receiver 23 (FIG. 1) is IR coupled to transmitter 21 and therefore detects the IR radiation from transmitter 21 (FIG. 1) and becomes active after delay 33 at t=t1 (45). When transmitter 21 (FIG. 2) is turned off at t=t2 (47), receiver 23 (FIG. 1) no longer detects the IR radiation from transmitter 21 (FIG. 1) and therefore becomes inactive after delay 35 at t=t3 (49). Due to the IR coupling between transmitter 21 (FIG. 1) and receiver 23 (FIG. 1), transceiver 19 (FIG. 1) cannot both receive data and transmit data at the same time. As a result, transceiver 19 (FIG. 1) is referred to as a half-duplex transceiver.
Delay 33 and delay 35 shown in FIG. 2 are a result of the finite response time of receiver 23 (FIG. 1). This response time may vary between any two IR transceivers due to component variability resulting from manufacturing. Delay 35 is referred to as the latency time for IR device 17 (FIG. 1) and is a characteristic of IR transceiver 19. The latency time for IR device 1 7 (FIG. 1) is therefore the minimum length of time an external IR device (communicating with IR device 17 over an IR communication link) must wait between receiving data from IR device 17 (FIG. 1) and subsequently sending data to IR device 17 (FIG. 1).
During the initialization stage of an IR communication link between IR device 17 (FIG. 1) and the external device, the two devices will "negotiate" to determine and exchange various parameters in order to enable the subsequent exchange of data. This is referred to as the negotiation stage. A parameter exchanged during the negotiation stage is a latency time parameter (LTP). The LTP for IR device 17 (FIG. 1) is transferred from IR device 17 (FIG. 1) to the external device. The LTP for IR device 17 informs the external device the time required to wait between receiving and subsequently sending data to IR device 17 (FIG. 1) to allow for the latency time of IR device 17. Likewise, the LTP for the external device is transferred from the external device to IR device 17 and informs IR device 17 the time required to wait between receiving and subsequently sending data to the external device to allow for the latency time of the external device.
As indicated previously, the latency time may vary between any two IR transceivers as a result of differences in components as they are manufactured. To account for these component variances, IR transceiver manufacturers typically determine and publish a maximum latency time for each class of IR transceiver. As the name implies, the maximum latency time is a value that represents the upper limit for the distribution of latency times of every transceiver that is of the same class.
Previously, the LTP for a device was based on the maximum latency time published for the class of transceiver used in the device. Even though the latency time of many transceivers of a given class in fact is below the maximum latency time for the class, these improved devices are not utilized to their optimum in these systems.